A new Carnegie Mellon study finds that the climate change and human health costs of owning and operating a plug-in electric vehicle in coal-heavy regions of the eastern United States have dropped significantly as coal-fired power plants that supply electricity to charge electric vehicles have been displaced by natural gas.

This shift has made electric and gasoline vehicle lifetime emissions costs comparable, but the open-access study, published in the ACS journal Environmental Science & Technology illustrates that where they go from here will depend on a few key factors.

Plug-in electric vehicles (PEVs) can reduce air emissions when charged with clean power, but prior work estimated that in 2010, PEVs produced 2 to 3 times the consequential air emission externalities of gasoline vehicles in PJM (the largest US regional transmission operator, serving 65 million people) due largely to increased generation from coal-fired power plants to charge the vehicles.

We investigate how this situation has changed since 2010, where we are now, and what the largest levers are for reducing PEV consequential life cycle emission externalities in the near future. We estimate that PEV emission externalities have dropped by 17% to 18% in PJM as natural gas replaced coal, but they will remain comparable to gasoline vehicle externalities in base case trajectories through at least 2035.

Increased wind and solar power capacity is critical to achieving deep decarbonization in the long run, but through 2035 we estimate that it will primarily shift which fossil generators operate on the margin at times when PEVs charge and can even increase consequential PEV charging emissions in the near term.

We find that the largest levers for reducing PEV emissions over the next decade are (1) shifting away from nickel-based batteries to lithium iron phosphate, (2) reducing emissions from fossil generators, and (3) revising vehicle fleet emission standards. While our numerical estimates are regionally specific, key findings apply to most power systems today, in which renewable generators typically produce as much output as possible, regardless of the load, while dispatchable fossil fuel generators respond to the changes in load.

—Bruchon et al.

Bruchon et al.

“People often think that growing wind and solar power are making electric vehicle charging cleaner. In the long run, that will likely become the case, but over the next decade of fleet transition, we find that the most important factors are shifting away from nickel-based batteries and tightening standards for emissions from fossil fuel power plants and the vehicle fleet.

—Jeremy Michalek, corresponding author

The PJM power grid region—the largest regional transmission operator in the US—stretches from Chicago to Philadelphia to North Carolina, and serves 65 million people in 13 states and the District of Columbia. The mix of power sources in PJM is similar to that of North America as a whole, and as such provides a baseline for broader assessment.

The research findings anticipate the continuation of reductions in electric vehicle emissions costs through 2025, after which they could stagnate, rise, or fall, depending on key factors such as the evolution of the power grid, battery technology, and public policy.

An interactive website created by Michalek’s coauthor and CMU engineering and public policy alumnus, Matthew Bruchon, allows users to compare the life cycle emissions of gasoline and electric vehicles under a range of scenarios to understand which factors matter most.

The authors find that shifting away from nickel-based batteries is one of the largest levers for reducing electric vehicle lifetime emissions over the next decade, because nickel production releases substantial sulfur dioxide emissions in some supplying countries and contributes to respiratory and cardiovascular disease. The study indicates that nickel-free battery alternatives, such as lithium iron phosphate, can reduce lifetime emissions costs.

The other key factor is public policy. Since adding new electric vehicle charging will primarily increase fossil fuel power generation over the next decade, emissions from fossil fuel plants play a large role in determining the emissions consequences of electric vehicle adoption. Federal car and truck emissions standards are also critical to determining what overall fleet emissions will look like.

—Jeremy Michalek

Resources

• Matthew Bruchon, Zihao Lance Chen, and Jeremy Michalek (2024) “Cleaning up while Changing Gears: The Role of Battery Design, Fossil Fuel Power Plants, and Vehicle Policy for Reducing Emissions in the Transition to Electric Vehicles” Environmental Science & Technology doi: 10.1021/acs.est.3c07098